Sound finder



April I1, 1939. R, w, MANm 2,153,933

SOUND FINDER Filed Oct. 6, 1957 INVENTOR. RzzcZz' W/YandZ BY W444 A TTORNEY Patented Apr. 11, 1939 UNITED s"ni'ri :s

FFlCE SOUNDFIINDER Rudi W. Mandi, New York, N. Y.

Application October 6, 1937, Serial No. 167,637

4 Claims. (01. 181-26) the selected sound to the receiver positioned ata suitable point within the box.

Sound finders of this general character so far 1 proposed have either their direction selectivity restricted to short sound waves, that is to high notes, or they require a very excessive bulk and extension. Furthermore, with these finders of the prior art, the focus is on the same side of the reflector as the sound source, and hence the receiver obstructs and shatters the incoming sound waves. This results also in an unsatisfactory arrangement of the apparatus: it becomes even more bulky, and the apparatus may become unsuitable, for instance, for simultaneously tak ing photographic pictures and sound records of an actor. Furthermore, withthese known finders, the focus is indistinctly determined for the reception of long sound waves, and hence the selectivity with respect to these becomes imperfect.

The present invention eliminates all these disadvantages. It is accordingly the object of the present invention, to provide for a relatively compact sound finder which is source selective through the entire range of audible sound waves. having a sharp selectivity with respect to said whole range, a finder with the receiver located oi the direction of the incoming sound.

All these advantages are obtained by the use of a strip shaped reflector. In principle, the reflecting wall portion has the shape of a portion of an ellipsoid of'revolution, which term ellipsold and ellipse will include in this specification and in the claims a paraboloid or a parabola respectively as a special case, the parabola being considered as an ellipse of infinite excentricity. The longitudinalextension of the strip is on a meridian of the ellipsoid, the width is on a zone of the ellipsoid. However, for practical purposes, it is sufficient and preferred, to ;suppress shaped reflector is not symmetric with .respect to the major principal axis of the ellipse, but it is unsymmetric thereto. In the preferred embodiment, the strip is cut out on one side of the major axis, so that it does not contain the apex point at the and of the major axis, and it extends about equally to both sides of that point of the ellipse at which the tangent forms an angle of 45 degrees with the two principal axes of the ellipse.

These and other advantages and character-' istics of the present invention will now be described in the specification, and a preferred embodiment will be illustrated in the drawing, it being understood that, since the principles of my invention can be incorporated in many specific devices, it is not intended to be limited to the ones here shown, except as such limitations are clearly imposed by the appended claims.

In the drawing, like numerals refer to similar parts throughout the several views, of which Fig. 1 represents an ordinarily horizontal cross section on line l-l of Fig. 2 through the sound box of a sound finder incorporating my invention,

Fig. 2 represents an elevational view of the finder seen from the line 22 of Fig. 1,

Fig. 3 is a diagram illustrating the shape of the reflecting wall portion of the' sound box,

Fig. 4 is a perspective view of the sound finder illustrating the use of a periscope or telescope for focussing the sound source,

Fig. 5 shows in a larger scale the preferred receiver used within the sound finder.

In Figs. 1 and 2, there is represented a sound I ,of smooth hard material, such as wood or metal,

and sound absorbing side walls I8 and I9. The latter comprise a grating 20 composed of narrow strips of metal or canvas, backed by a wall 2| of sound deadening material such as felt 1 or cork. broadly.

' Top I4 and bottom l5 are preferably parallel and spaced about 1 foot apart. In Fig. 3, the shape of reflector I1 is illustrated. The surface of I! is substantially a cylinder over a segment ellipse. I use only the portion ll of the ellipse 22 represents a microphone receiver of an elliptical line, 3i representing the entire situated between and spaced from the apex or end of the major axis 32 and the end of the minor ams 33, said portion preferably including the point 34 of the ellipse, the tangent AB of which forms an angle of 45 degrees with the major axis through the foci 22' and 35, and hence also with the minor axis of the ellipse. The receiver 22 is located adjacent one focus of the ellipse, and is exposed to the sound waves ema= nating from the other focus 35. In'practice, the excentricity from 22 to 35 is rather long, andthe ellipse approaches the shape of a parabola.

The sound absorbing side wall portions 88, 59 form a broken line, the inner boundaries following straight lines connecting the foci with the end points of the reflector ll. At the ends of the opening it, reflector flanges 23 are provided for increasing the selectivity of the finder.

Fig. 4 illustrates the use of the finder. During the taking of a sound picture, (for instance), perlscope M rigidly fastened to the finder box W is directed towards the source of the sound intended for recordation. The box is accordingly turned by the hand wheel l3, and, if necessary,

it may be tilted by the use of the adjustable screws I 2. Turning only will generally be sufflcient. The reflector ill of the box has to be about 10 feet large, if the selectivity shall include all sound waves of the audible range. comes somewhat smaller if the deepest notes are dispensed with. The recording device will then preferably be made unresponsive to such deep notes.

Fig. illustrates the receiver used. It is peculiar by its flattened or compressed mouth piece it, which opens in a slot 72. This extends at right angles to top and bottom 85 and it, and practically all the way from top to bottom. It may be desirable to use a mouth piece it with a hinged door member 13 fastened to the stationary portion thereof. Door it may be turned by any means, not shown, whereby the selectivity of the device will be changed.

I claim:

1. 4 mobile sound finder box having a pair of substantially plane and parallel side walls, a, pronouncedly elongated strip-shaped sound refleeting wall in its crosswise direction substantially straight and at rightangles to saidside walls-..

and following in its lengthwise extension the contour of an ellipticarc connecting a firstpoint of It be-' pronouncedly elongated strip-shaped soundTefiecting wall in its crosswise direction substantially straightand at right angles to said side walls and following in its lengthwise extension the contour of an elliptic arc connecting a first point of an ellipse spaced from the apex thereof with a second point spaced farther thereof, said are being inclined under 45 degrees towards the principal axes of the ellipse at one of its points, and a sound sensitive electric receiver within'the box adjacent the focus of said elliptic arc.

3. A mobile sound finder box having a pair of substantially plane and parallel side walls, a pronouncedly elongated strip-shaped sound reflecting wall in its crosswise direction substantially straight and at right angles to said side walls and following in its lengthwise extension the contour of an elliptic arc connecting a first point of an ellipse spaced from the apex thereof with a second point spaced farther thereof, said are being inclined under 45 degrees towards the princlpal axes of the ellipse at one of its points near its center, and a sound sensitive electridreceiver within the box adjacent the focus of said elliptic are. r Y

4. A sound finder box having a plane top wall, a plane bottom wall parallel to said top wall, a sound reflecting side wall at right angles to said top and bottom following through a distance substantially longer than the distance between said top and bottom the contour of an elliptic are connecting a first point spaced from the apex of the generating ellipse with a second point spaced farther from said apex and being inclined at one of its points under degrees towards the principal axes of said ellipse, plane sound absorb- 

